KR20190100408A - Combination of Multiple Effect Distillation and Multistage Flash Evaporation Systems - Google Patents

Combination of Multiple Effect Distillation and Multistage Flash Evaporation Systems Download PDF

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KR20190100408A
KR20190100408A KR1020197023692A KR20197023692A KR20190100408A KR 20190100408 A KR20190100408 A KR 20190100408A KR 1020197023692 A KR1020197023692 A KR 1020197023692A KR 20197023692 A KR20197023692 A KR 20197023692A KR 20190100408 A KR20190100408 A KR 20190100408A
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flash evaporation
brine
effect
effect distillation
combination
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KR1020197023692A
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KR102068530B1 (en
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에삼 엘-딘 패러그 엘세이드
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쿠웨이트 인스티튜트 포 사이언티픽 리서치
쿠웨이트 인스티튜트 포 사이언티픽 리서치 글로벌 페이턴트 트러스트
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D3/00Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/06Flash distillation
    • B01D3/065Multiple-effect flash distillation (more than two traps)
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D3/00Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/14Fractional distillation or use of a fractionation or rectification column
    • B01D3/143Fractional distillation or use of a fractionation or rectification column by two or more of a fractionation, separation or rectification step
    • B01D3/145One step being separation by permeation
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D1/00Evaporating
    • B01D1/26Multiple-effect evaporating
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D3/00Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/06Flash distillation
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D3/00Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/14Fractional distillation or use of a fractionation or rectification column
    • B01D3/143Fractional distillation or use of a fractionation or rectification column by two or more of a fractionation, separation or rectification step
    • B01D3/146Multiple effect distillation
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D5/00Condensation of vapours; Recovering volatile solvents by condensation
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D5/00Condensation of vapours; Recovering volatile solvents by condensation
    • B01D5/0033Other features
    • B01D5/0054General arrangements, e.g. flow sheets
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D5/00Condensation of vapours; Recovering volatile solvents by condensation
    • B01D5/0057Condensation of vapours; Recovering volatile solvents by condensation in combination with other processes
    • Y02A20/128

Abstract

The combination of the multi-effect distillation and multi-stage flash evaporation system 10 integrates the multi-stage flash (MSF) evaporation system 200 with the multi-effect distillation (MED) system 100 so that the MSF process moves upwards in the temperature range and the MED distillation The process operates in the low temperature range. The multistage flash evaporation system 200 includes a plurality of flash evaporation / condensation steps, so that the multistage flash evaporation system 200 receives a large amount of seawater or brine from an external source and generates distilled water. The multiple effect distillation system 100 includes a plurality of condensation / evaporation effects 18, which receive concentrated brine from the multistage flash desalination system 200 and produce distilled water.

Description

Combination of Multiple Effect Distillation and Multistage Flash Evaporation Systems

The present invention relates to desalination, and more particularly to a system for producing desalted water from brine such as seawater using both multi-effect distillation and multistage flash evaporation.

Falling film evaporators are industrial devices that concentrate solutions, especially with heat-sensitive components. Evaporators are a special type of heat exchanger. Generally, evaporation occurs on the outer surface of the horizontal or vertical tube, but in some cases the process fluid evaporates inside the resin tube. In all cases, the process fluid to be evaporated flows down by gravity as a continuous membrane. The fluid runs downward along the tube wall and is called a "falling film."

In falling film evaporators, the fluid distributor must be carefully designed to maintain a uniform liquid distribution across all tubes in which the solution falls. In most instruments, the heat medium is disposed inside the tube, thereby obtaining a high heat transfer coefficient. To meet this requirement, condensation vapor is generally used as the heat medium.

In the case of internal evaporative fluids, separation between the liquid phase (ie solution) and the gas phase occurs inside the tube. As this process proceeds, the downstream vapor velocity increases to maintain mass conservation, thereby increasing the shear force acting on the liquid membrane and thus the velocity of the solution. As a result, higher membrane velocities of thinner and thinner membranes can lead to a gradual increase in turbulence. This combination of effects allows for a very high heat transfer coefficient.

The heat transfer coefficient on the evaporation side of the tube is largely determined by the hydrodynamic flow conditions of the membrane. For low mass flows or high viscosities, the membrane flow can be laminar, where heat transfer is controlled by conduction through the membrane. Thus, in this condition, the heat transfer coefficient decreases with increasing mass flow. With increased mass flow, the membrane becomes wavy laminar and turbulent. Under turbulent conditions, the heat transfer coefficient increases with increased flow rate. Evaporation typically occurs at very low average temperature differences between the thermal medium (ie, process stream) between 3 K and 6 K and the membrane liquid, making such devices ideal for heat recovery in multiple effect processes.

Another advantage of falling film evaporators is that the residence time of the liquid is very short and there is no overheating of the liquid. The residence time inside the tube is usually measured in seconds, making it ideal for heat sensitive products such as milk, fruit juice, pharmaceuticals, and other mass produced liquid products. Falling film evaporators are also often used in the field of deep vacuum applications because they feature very low pressure drops.

However, since the membrane liquid is in intimate contact with the heating surface, such an evaporator is susceptible to contamination from the settling solids; In general, low liquid velocities in the top row of horizontal tube banks are usually not sufficient to effect effective self cleaning of the tubes. Thus falling film evaporators are generally used only in liquids that are clean and do not settle.

Falling film evaporators are the main principle used in multi-effect distillation (MED) systems (sometimes referred to as "multi-effect distillation systems"). Multi-effect distillation is a distillation process often used for seawater desalination. It consists of multiple stages or "effects". In each effect, the seawater supplied is filmed on the outer surface of the tube and heated by steam inside the tube. The falling water film evaporates, and this steam flows into the tube of the next effect, heating and evaporating more water. Each effect basically reuses the energy of the previous effect. The tube may be submerged in the feed, but the supplied sea water is sprayed onto the horizontal tube bank and then water droplets flow from the tube to the tube and collect at the bottom of the effect.

2 illustrates a typical prior art multi-effect distillation evaporator 100.

In the first effect 102, seawater is supplied through the inlet 108 to one or more sprays or nozzles 110 located within the first effect 102. The heated steam generated by an external boiler or the like is supplied through the tube 112. As the injected seawater falls on the outer surface of the tube 112 and forms a thin liquid film thereon, the heat transferred from the heated vapor evaporates the seawater to form water vapor (V). The heat transfer cools the steam and produces condensed water in the tube 112, which is then returned to the boiler for reheating. Seawater that has not evaporated (indicated by S in FIG. 2) is transferred from part of the tube 11 to another part (or if a plurality of such tubes are used) until they are collected at the bottom 114 of the first effect. Drop the water droplets). The pump 116 delivers this collected seawater to the second effect 104 sprayed by the spray or nozzle 120 similar to the spray in the first effect 102.

Water vapor (V) in the first effect acts in a similar manner to the vapor delivered by the second tube (118) to the second effect and passes through the tube (112) in the first effect, but condensation of the second tube (118) No water is returned and the water supplied to the boiler is withdrawn through the product conduit 124 where distillation is collected. Seawater S that does not evaporate into water vapor V in the second effect 104 falls back from the tube portion (or tube to tube) to the tube portion to be collected on the bottom 122 of the second effect 104. The pump 126 delivers this collected seawater to a third effect 106 that is sprayed by the spray or nozzle 128 similar to the spray in the first and second effects 102, 104.

Water vapor V from the second effect 104 acts in a manner similar to the vapor that is delivered by the third tube 130 to the third effect 106 and passes through the tube 112 at the first effect 102. , In a second effect 104 acts in a manner similar to the heat steam passing through the second tube 118. In the third effect 106, the condensate in the third tube 130 is drawn through the product conduit 124 and mixed with the desalted water from the second effect 104 to be collected. Sea water (S) that does not evaporate to water vapor (V) in the third effect (106) falls back from the tube portion (or tube to tube) to the tube portion to be collected at the bottom 132 of the third effect (106), the pump 134 is pumped into the next effect. Although only three effects 102, 104, 106 are shown in FIG. 2, it should be understood that this is shown for illustrative purposes. An example of a conventional multi-effect distillation system is disclosed in US Pat. No. 3,481,835, which is incorporated herein by reference.

As mentioned above, conventional multi-effect distillation systems that rely on general falling film evaporation have a number of disadvantages, each of which generally limits the design capacity and maximum allowable operating temperature of the unit. At large levels, many MED designs have complex and often circuitry paths for heated seawater and steam to minimize pump usage, maintain tube wetting to avoid scaling, and maximize energy recovery from flashing brine and distillate. It includes. As pumps, vessels, waterways and steam paths are optimized at the minimum path, the design suffers from excessive losses.

In addition to multi-effect distillation systems, multistage flash (MSF) evaporation is also relatively commonly used to produce demineralized water from seawater sources such as seawater. 3 shows a prior art MSF system or plant 200 in which feed seawater or brine enters the system under pressure and enters the plant 200 via a pump 228 or the like. The seawater or brine is transferred under pressure to the brine heater 214 through conduits or pipes 232 and then transfer the heated brine to the flash chamber 216. Steam generator 212, a separate, simple steam power plant outside the MSF system, supplies the brine heater 214 with the heating steam needed to heat the brine. The steam generator 212 is a simple steam power plant (preferably a Rankine cycle power plant) and consists of a pump 240, a boiler 242 and a steam turbine 244 in addition to the condenser 214, and also serves as a brine heater. It is to be understood that the steam turbine 244 shown in FIG. 3 is not a component of a typical MSF process, but is merely shown as part of an exemplary installation utilizing MSF. Steam passing through the brine heater 214 may be extracted from a turbine, such as steam turbine 244, or may be supplied directly from boiler 242. It should be understood that the simplified description of FIG. 3 is provided to illustrate a conventional MSF process and system. Typically, the superheater may also be used to regulate the steam so that the steam is saturated and not overheated, whether extracted from the turbine or passed directly from the boiler before entering the brine heater 214. Conventional MSF systems are well known. US Pat. Nos. 3, 966,562 and 8,277,614, which are incorporated by reference in their entirety herein, refer to conventional MSF systems.

As shown, seawater or brine may first be discharged through the cooler 230 to lower the feed temperature of the final stage. The brine passes through feed heater conduit 232. The feed heater is a condenser type heat exchanger where the feed is heated by the heat released by condensing the flashed vapor at each stage. The brine supplied reaches the first stage at high temperature but is not high enough to start flashing, so additional heat must be supplied to the brine. The brine heater 214 receives steam from the external steam generator 212 and raises it to a level suitable to begin flashing the brine temperature. The brine is then injected into the flash chamber 216. The number of flash chambers 216 shown in FIG. 3 is shown for illustrative purposes only and it should be understood that the number of flash steps is simplified. Typical MSF installations have 15 to 40 steps or flash chambers. The brine delivered by the heater 214 generally has a temperature of approximately 90 ° C. to 120 ° C., depending on the chemical treatment or anti-scaling technique used, the quality of the heated vapor and the discharge system maintaining the pressure at each stage.

The operating pressure of the flash chamber 216 is lower than the operating pressure of the heater, causing the heated brine to boil or "flash" quickly with steam. Typically, this water is only converted to steam in a small proportion. As a result, the remaining water will be sent through a series of additional steps or flash chambers 216 having a lower working pressure than each previous chamber as shown. The brine is delivered to the stage through each successive flash chamber 216 or through any conventional method. When steam is produced, it condenses in the same stage or flash chamber on pipe 232 through each chamber. Condensate is collected by collection tray 218 and removed by pump 220 to produce desalination stream 222. Pipe 232 and tray 218 form a condenser for each flash step. Residual brine having a high brine concentration may be discharged by a separate pump 224 and removed as waste at 226.

In the MSF process, the heat transfer surface on the brine side never undergoes a phase change and is always kept wet and relatively unscaled by effective scale control techniques involving chemical treatment of feed water and online machine cleaning. Flashing of the brine occurs at a safe distance from the heat transfer tube. This procedure significantly protects the MSF process from the scale formation and precipitation to the temperature at which the sulfate based scale begins to form (ie, above 121 ° C.).

On the other hand, in the MED process, evaporation occurs directly on the outer surface of the heat transfer tube as the brine film reaches the liquid superheat temperature required for phase change to occur. This evaporation mechanism makes the heat transfer surface very susceptible to scale formation and precipitation, especially since only chemical treatment can be used to delay scale formation while online mechanical cleaning is not possible. This situation imposes strict limits on the maximum actual operating temperature in the MED process and must be kept within a safe range (ie below 70 ° C).

Conventional MSF processes suffer from three major causes of thermodynamic losses: loss of boiling point rise, loss of pressure drop and loss of equilibrium. Boiling point rise loss is caused by the presence of high concentrations of salt in the brine, which is a loss that must be present in all processes, including boiling points or phase changes, the value of which depends on the state of the brine in terms of temperature and concentration of the brine solution. . Loss of boiling point rise increases with temperature and concentration. In the MSF process, when the brine flows into the cold phase, the concentration increases as the brine temperature decreases, so the two driving forces of boiling point rise are reversed. As a result, this result minimizes the boiling point rise in the MSF step.

The pressure drop caused by the steam flow through the demisters and through the tube bundles results in vapor expansion, which is accompanied by a drop in the corresponding saturation temperature. This is called the pressure drop loss, which is much smaller in size and increases as the brine flows to a lower temperature stage compared to the break point rise or non-equilibrium loss. Non-equilibrium loss is a characteristic derived from the MSF process, unlike the previous two losses. The amount of this loss is inversely proportional to the step heat level and directly proportional to the flashing brine depth. To account for this characteristic, the steam equilibrium temperature of the brine pool at a given depth below the surface is measured.

Figure pct00001
Can be defined as
Figure pct00002
Steam equilibrium temperature,
Figure pct00003
Represents the rate of change of the steam saturation temperature.
Figure pct00004
Is the given depth below the surface
Figure pct00005
Represents the hydrostatic pressure of the brine pool.

4 is another for typical flashing range of a typical MSF process.

Figure pct00006
In value
Figure pct00007
Show the plot for. 4 shows that the effect of the brine depth on the steam equilibrium temperature of the brine pool is not of great importance at the high heat level stage but rapidly at the low heat level stage. In other words, the brine bulk temperature at the step inlet and outlet is less than the boiling point rise.
Figure pct00008
And
Figure pct00009
If you take
Figure pct00010
Is the maximum evaporation at any point on the brine surface
Figure pct00011
It is a necessary condition until the depth of. For high heat level stages, this condition is usually provided for maximum submersion in the brine reservoir. However, the conditions for maintaining significant depth in the brine pool if evaporation is effectively maintained as the brine moves through the stage towards the outlet
Figure pct00012
This should be maintained. Conditions when brine flows to a low heat level stage
Figure pct00013
end

It is also spread at minimum brine concentrations, which evaporation can only occur near the surface at the stage inlet, and diminish as the brine approaches the stage outlet, thus making much of the stage unproductive.

5 is a plot of three losses and the resulting total thermodynamic loss along stages of a conventional prior art MSF unit. FIG. 5 shows the relative magnitude change in this loss as part of the total mean temperature difference between flashing brine and recycling brine along the stages of the MSF apparatus. Unlike MSF, non-equilibrium thermodynamic losses do not exist in the MED process. This is because evaporation occurs in the superheated liquid film, not the flash of the liquid pool. On the other hand, boiling point rise and pressure drop losses are present at levels similar to those of the MSF process. However, this loss is much less important when it comes to the thermal performance of the MED process, and the main reason is that the evaporation temperature range is already limited to narrow cold stretching, and this low heat level overall heat transfer coefficient is almost twice that of the MSF process. Because it becomes.

The combined effect of this loss is illustrated by the stepwise and cumulative mass flow rates of the product distillation of FIG. 6 shown for a typical prior art MSF unit. 6 clearly shows that step productivity depends directly on the step heat level and that low step productivity is an essential characteristic in the low temperature region step of the MSF process.

When considering an MSF or MED plant, the first two basic quantities must be established: the available thermal energy in the form of lower steam required to run these plants in order to produce the plant's production capacity and desired output. Guidelines for measuring MSF and MED plant efficiency or process potential are generally based on these two quantities and are known as gain output ratio (GOR) or performance ratio (PR). GOR is defined as the mass ratio of product effluent (kg per unit time) and steam fed to the process (kg per unit time). PR is defined as the quantity measured in kilograms per predefined amount of latent heat due to condensation of heated steam, or the amount of heat supplied in kilograms to produce one kilogram of distillate. These ratios depend on several parameters, some of which include the highest brine temperature (TBT), the number of evaporation steps or effects, the range of flash temperatures used, the mass ratio of the brine to be evaporated and the product distillate, brine concentration and evaporation steps. Or the effectiveness of the effect. However, there are technical and economic constraints on the upper limit of GOR or PR. However, care must be taken when comparing these amounts (GOR or PR) to the amount of MED for MSF, as the heating steam conditions and the energy ratings supplied to each process are generally different. It is desirable to be able to integrate the MSF with the MED so that the flashing temperature range of the MSF process moves up on the temperature scale to improve the performance of the MSF at relatively high operating temperatures, but the MED subunit is more integrated in this range integrated into the MSF system It operates in a lower temperature range for better performance. Accordingly, there is a need for a combination multi-effect distillation and multi-stage flash evaporation system that solves the above problems.

The combination multi-effect distillation and multi-stage flash evaporation system incorporates a multi-stage flash (MSF) evaporation system and a multi-effect distillation (MED) system so that the MED distillation process operates at a lower temperature range (eg below 70 ° C), Allow the flashing temperature range to move up on the temperature scale (eg 70-120 ° C). The multistage flash evaporation system includes a plurality of flash evaporation / condensation steps to receive a stream of brine (eg seawater or brine) and produce pure distilled water after the multistage flash evaporation system is preheated by the feed heater of the multifunctional distillation system. The multiple effect distillation system includes a plurality of condensation / evaporation effects such that the multiple effect distillation system receives concentrated brine heated in a multistage flash evaporation system for further distillation and produces pure distilled water.

The brine heater is in fluid communication with the multistage flash evaporation stage and the first heating steam with the brine heater to further heat the brine stream after the brine stream is preheated by the multi-effect distillation system and the feed heater of the evaporation stage of the evaporation multistage flash evaporation system. A boiler is provided for conveying this. The first desuperheater may be provided for selectively cooling and conditioning the first stream of heated steam prior to injecting the brine heater. Preferably, the first portion of the condensation steam produced by the brine heater is recycled for use in the first desuperheater. The second portion of the condensation steam produced by the brine heater can be recycled for use in the boiler.

Seawater is delivered from an external source, and a pretreatment system is provided to filter the seawater before delivering the seawater to the feed heater of the multiple effect distillation system. The pretreatment system can optionally include, for example, low pressure microfiltration or ultrafiltration membrane systems and nanofiltration membrane systems. In addition, a second desuperheater may be provided for selectively cooling and conditioning the second heated steam prior to injection into the first steam of the plurality of distillation effects of the multi-effect distillation system. The second heating steam may be produced by the boiler. A brine circulation pump is also provided between the multi-stage flash evaporation system and the multi-effect distillation system such that the first portion of uncondensed concentrated brine delivered by the pump is mixed with the pretreated and then circulated back to the multistage flash evaporation system. Preheated seawater forms a continuous brine stream for further heating, flashing and condensation in a multistage flash evaporation system. The second portion of concentrated brine not evaporated is passed to the first portion of the plurality of distillation effects of the multiple effect distillation system for further distillation. In addition, in the last stage of the multistage flash evaporation system, the pure distillation stream is withdrawn and delivered to the first portion of the plurality of receptacles in the multistage distillation system to further flash and recover the available latent heat of the pure distilled water.

In one embodiment, the thermal vapor compressor is in fluid communication with the last one of the plurality of evaporation effects of the multiple effect distillation system such that the thermal vapor compressor produces a second heated steam. Thermal steam compressors are operated by relatively medium / low pressure steam provided by the boiler. In another embodiment, the mechanical steam compressor is in fluid communication with at least one of the last flash evaporation steps to inject heating steam into the brine heater rather than using heating steam from the boiler. Such features of the invention may become more apparent according to the following specification and drawings.

1 schematically shows a combination of a multi-effect distillation and multistage flash evaporation system according to the present invention.
2 schematically illustrates a conventional multiple effect distillation system.
3 schematically illustrates a conventional multi-stage flash evaporation system.
4 is a graph showing a plot of vapor equilibrium temperature of a brine pool at a given depth below surface for various depths beyond the typical flashing range for a conventional multi-step flash evaporation process.
FIG. 5 is a graph showing plots of boiling point rise loss, pressure drop loss and non-equilibrium loss with the resulting total thermodynamic loss over the stages of a conventional multi-stage flash system.
FIG. 6 is a graph showing the combined effect of the losses of FIG. 5 shown in staged and cumulative mass flow rates of product distillate for a conventional multistage flash evaporation system.
7 schematically illustrates an alternative embodiment of a combination of a multiple effect distillation and multistage flash evaporation system.
8 schematically illustrates another alternative embodiment of a combination of a multiple effect distillation and multistage flash evaporation system.
Like reference numerals refer to corresponding features throughout the accompanying drawings.

The combination 10 of the multi-effect distillation and multi-stage flash evaporation system shown in FIG. 1 uses a multi-effect distillation (MED) system similar to the MED system 100 of FIG. 2 to a multi-stage flash similar to the MSF evaporation system 200 of FIG. (MSF) combined with the evaporation system. The multi-stage flash evaporation portion of the system 10 shown in FIG. 1 begins with a mixture of seawater feed and recycle concentrated brine entering the system under pressure entering the conduit or pipe 32 via a mixer 68 or the like. Seawater feed is introduced from an external source by a pump 28 and passes through the final condenser 24 of the multiple effect distillation portion of the system 10 as described in detail below. Prior to injection into the MSF process, the total volume (or alternatively only the first portion) of the seawater feed is preferably pretreated by passing through filtration system 40 using a nanofiltration (NF) membrane or the like. Selective flow control of the first portion of the seawater feed through the filtration system 40 may be provided by any suitable type of valve 46. As shown in FIG. 1, the second portion of the seawater supply bypasses filtration system 40 through any suitable type of valve 42. Filtration system 40 may optionally be combined with secondary low pressure microfiltration (MF) or ultrafiltration (UF) membrane filtration system 44. Untreated seawater or reject brine from the filtration system 40 may be discharged to the system through the outlet 48. The pretreated seawater is then passed through the feed heater 20 of the multi-effect distillation portion of the system 10 to the MSF portion of the system 10 as described in detail below. It is to be understood herein that seawater, other types of seawater, for example brine, can be treated by multiple effect distillation and multistage flash evaporation systems.

The pretreated, preheated seawater stream is joined to the first portion of the concentrated brine stream recycled from conduit or pipe 64 and then the two streams are mixed together in a mixer 68 or the like. The mixture of seawater and brine is transferred to the brine heater 14 through conduits or pipes 32 under pressure, and then transfer the heated brine to the flash chamber 16. Boiler 12, which burns the fuel to thermally regenerated condensate with additional make-up water, acts as a steam generator to supply the brine heater 14 with the heating steam needed to heat the brine. After heat transfer to the brine, the steam is condensed and the condensate is returned to the boiler 12 for recycling to steam along the conduit or pipe 52. The condensate is pressurized by the pump 50. In addition, a thermostat 54 may be provided as shown. The desuperheater 54 injects a controlled amount of cooling water (ie condensate selectively condensed by the pump 50 via a pipe or conduit 56) into the superheated steam stream to reduce or control the steam temperature. Used.

Flash chamber 16 acts in a manner similar to that of the conventional MSF system 200 of FIG. 3 to produce desalted distilled water, which is discharged from the MSF portion by pipe or conduit 58. Recirculation pump 60 passes a first portion of concentrated brine under control of valve 62 through a recycle pipe or conduit 64 to mix with preheated seawater pretreated at 68. The remainder of the concentrated brine enters the feed water inlet 36 of the MED portion of the system 10 under the control of the valve 66.

The MED portion includes multiple effects 18 that operate in a similar manner as the conventional multiple effect distillation evaporator 100 of FIG. As shown in FIG. 1, a portion of the steam produced by the boiler 12 may be diverted along the pipe or conduit 70 to supply heated steam to the steam chest of the first effect. A thermostat 72, similar to the thermostat 54, may be provided to the pipe or conduit 70, with a portion of the condensate delivered through the pipe or conduit 74 and pressurized by the pump 76.

The heated steam for each additional effect of the MED portion is provided from the steam generated in the previous effect after passing through the feed heater 20 to heat some of the brine introduced from the feed water inlet 36 into steam. Steam condensed from each effect 18, which is demineralized water, is collected in each receptacle 22 via a pipe or conduit 26, and the first receptacle is taken from the MSF portion of the system 10 via a pipe or conduit 58. Accept distillate. From the final effect the steam passes through the final condenser 24. After condensation in the final condenser, the condensate is mixed with the distillate stream from the last receptacle 22 via a pipe or conduit 34 to form the final distillate product (ie, demineralized water), which is fed to the distillate pump 80. Is removed by Reject brine is removed from the final effect 18 by the pump 78. Receptacle 22 is preferably fed to each flashing port associated with a particular effect, such as a distillate from the MSF portion, with distillate from each subsequent effect of the MED portion, where the pressure in the flashing port is maintained at a particular vacuum to distill Allows flashing of water to occur at the desired rate. For example, the pressure of the first port of the first flash port of the plurality of flash ports is equal to the pressure of the first effect through the pipe or conduit 30, and the first flash port is used to connect the pipe or conduit 58. Distillate is received from the MSF portion of system 10 through. The pressure of the second flash port is equal to the pressure of the second effect through the pipe or conduit 30, the second flash port passing the pipe or conduit 26 together with the undistilled distillate from the first flash port. To receive distillate from the first effect. This process continues until the pressure of the last flash port is equal to the pressure of the final condenser 24 through the pipe or conduit 30. The last flash port distills the remaining unevaporated distillate from the previous flash port from the last effect via pipe or conduit 26.

System 10 moves the flashing temperature range of the MSF process up on the temperature scale while integrating the MED subunit into the MSF system at the low temperature range. Typical MSF plants operate at flashing conditions in the temperature range of about 40 ° C to 90 ° C. However, in system 10, while maintaining a flashing span similar to 50 ° C., the same MSF portion of system 10 can be operated at a flashing temperature range between 60 ° C. and 110 ° C., and an additional MED part. The low temperature range between 40 ° C and 60 ° C is left behind. Effectively, this is an extension of the flashing temperature range, which is similar to the high temperature operation of some MSF plants, but the use of the flash temperature range, the patented lower temperature range, is much better.

In FIG. 1, the MED portion operates on the cold side of the system 10. As mentioned above, part of the concentrated brine from the MSF and the entire MSF product distillate are continuously boiled and flashed through the MED portion to generate steam, while the remainder of the concentrated brine continues to produce, while the remainder of the concentrated brine is Is mixed with makeup feed seawater and regenerated in the MSF section. Apart from the necessary changes in process temperature and pressure gradients, the MSF process of system 10 is relatively unchanged from conventional MSF systems except for the heat removal section of conventional systems that are no longer needed in system 10. It should be noted that it stays in the state. Instead, a heat removal step is added to the heat recovery section.

In the embodiment of Figure 7, heat is recycled in the MED portion. In FIG. 7 the vapor of the lowest temperature effect 18 and the vapor flashed in the last receptacle 22 are recycled by a thermal steam compressor (TVC) 84 and used as a heated steam to induce a first effect. In the embodiment of Figure 8, heat is recycled in both the MED and MSF portions. The system in FIG. 8 operates in a similar manner to the system of FIG. 7, but an additional amount of steam generated in the last few steps of the MSF is used to replace the heated steam supplied to the brine heater 14. In FIG. 8, this is shown to be performed by a mechanical vapor compressor (MVC) 82, but it should be understood that any suitable type of compressor including TVC may be used in this recycling process.

In the embodiment of Figures 7 and 8, the MSF portion is of recycle type, but the heat removal step is combined with a heat recovery step. The MED portion still operates in a conventional manner, where the feed water is heated in the MED feed heater 20 and then mixed with recycle brine to further heat until the brine heater 14 is reached in the MSF step 16. The portion of concentrated brine discharged from the MSF portion is fed to the first MED effect for further boiling, flashing, and evaporation.

Distillate from the MSF portion is fed to the first flashing port 22, where the pressure therein is maintained at the vacuum of the first effect, causing flashing of the distillate to occur at the desired rate. The steam released by flashing the distillate is passed through each feed heater 20 to join the steam that heats the feed. The brine removal from each effect 18 operating on the hot side of the system is transferred to subsequent effects to allow for further boiling, flashing and steam generation. Similarly, the product distillate of each effect 18 can then be passed to a cold flash port 22 to recover excess heat by partial flashing. The steam discharged from the last effect 18 can be delivered to the final condenser 24 where it is condensed, so that the lowest pressure is a thermal steam compressor (TVC) 84 as in the embodiment of FIGS. 7 and 8. Can be compressed or reused in a similar manner.

To illustrate the combination of a multi-effect distillation and multi-stage flash evaporation system 10, Tables 1 and 2 below show conventional MED and MSF compared to a thermally operated MED-MSF combination system (ie, the embodiment of FIG. 1). Sample performance characteristics of the system; A TVC driven MED portion and a thermally driven MSF portion of the combination MED-MSF desalination system (ie, the embodiment of FIG. 7); And a TVC driven MED portion and an MVC driven MSF portion of the combination MED-MSF desalination system (ie, the embodiment of FIG. 8). Process performance indicators include equivalent gain output ratio (GOR) per unit mass of distillate per unit mass of equivalent amount of heated steam (eg kg of distillate / kg of equivalent heating steam), and total energy input of kWh per tonne of distillate ( Heat and electricity), total energy input in kWh per tonne of distillate (including the sum of all practically useful energies based on the second law of thermodynamics) and product recovery (total seawater supply including distillate / seawater replenishment or distillate / cooling) Water). As can be seen in Tables 1 and 2, the GOR is much higher for the combination of embodiments of the MED-MSF desalination system compared to conventional MED processes and conventional MSF processes. In addition, energy input and exergy input are much lower in the MED-MSF combination desalination system compared to conventional MED processes and conventional MSF processes. The most important of these indicators is exergy input, which shows that the thermally driven MED-MSF composition is the most efficient in all three examples. In addition, in terms of water recovery, the MED-MSF combination is clearly superior to conventional MED processes and conventional MSF processes. Product recovery for the thermally driven MED-MSF combination system is highest in all three embodiments of the MED-MSF combination system. These high performance and high water recovery rates allow MED-MSF desalination systems to outperform other systems and technologies in terms of operating and overall product water costs.

Comparison of Conventional MSF and Combination MED-MSF Desalination Systems System description Number of steps or effects TBT o C  Of
Last stage or effect temperature
o C
heating steam o C TVC  Motif Steam o C
MSF MED MSF MED MSF MED MED Conventional MED System
(Figure 2)
N / A 9 N / A 75/40 N / A 80 N / A
Conventional MSF System
(Figure 3)
19 N / A 90.6 / 40.6 N / A 100 N / A N / A
Conventional MSF System
(Figure 3)
23 N / A 110 / 40.6 N / A 120 N / A N / A
Combination MED-MSF System (Figure 1) 19 9 110 / 76.3 76.3 / 40 120 82.2 N / A Combination MED-MSF System (FIG. 7) 19 9 110 / 76.4 76.4 / 40.5 120 N / A 141.68 Combination MED-MSF
Stem (Figure 8)
19 9 110 / 82.2 82.2 / 46 N / A N / A 141.68

Comparison of Conventional MSF and Combination MED-MSF Desalination Systems System description Equivalent GOR (Equivalent
GOR )
( Distillate  Kg /
Steam Kg)
Performance ratio (
Performance Ratio) ( Distillate  kWh / ton)
Exergy  Input (
Exergy  Input) (heat + pump, Distillate  kWh / ton)
Product Water Recovery Ratio
( Distillate  ton / seawater ton)
Conventional MED System
(Figure 2)
7.71 82.87 11.56 0.398 / 0.0675
Conventional MSF System
(Figure 3)
7.14 316.97 61.37 0.3745 / 0.0914
Conventional MSF System
(Figure 3)
8.9 248.22 58.61 0.3745 / 0.1149
Combination MED-MSF System (Figure 1) 10.57 57.79 3.69 0.495 / 0.107 Combination MED-MSF System (FIG. 7) 9.48 52.8 8.0 0.388 / (N / A) Combination MED-MSF
Stem (Figure 8)
15.4 58.6 14.73 0.4762 / (N / A)

It is to be understood that the present invention is not limited to the foregoing embodiments, but includes all the embodiments within the scope of the following claims.

Claims (19)

  1. The multi-stage flash evaporation system includes a brine heater, a plurality of flashing and condensation stages, the multi-stage flash evaporation system receives a certain amount of sea water from an external source, generates distilled water by sequential flashing effect, and converts the brine and distilled water into one stage Pass to the next step, and finally deliver the brine to the multiple effect distillation system for further evaporation in the last flashing step; And
    The multi-effect distillation system comprises a plurality of condensation, evaporation effects and a final condenser, the last stage of the multi-effect distillation system receives the brine from the multi-stage flash evaporation system to perform further evaporation by boiling the membrane, To produce a distillate; And
    The seawater supplied to the multi-stage flash evaporation system at ambient temperature is heated to the maximum permissible temperature without the formation and precipitation of sulfate scales (salts) while the brine and demineralised distillate loses minimum temperature dependent non-equilibrium Cooled by a sequential efficient flashing effect having an exit from the last flashing step at a temperature approximately midway between the ambient temperature and the maximum allowable temperature; And
    The brine enters the first effect of the multi-effect distillation system and continues to evaporate sequentially by efficient membrane boiling without loss of equilibrium; and
    From the final effect, steam condenses in the last condenser, which is the main heat sink in the combination system, and the brine exits the last effect of the multi-effect distillation system at a temperature very similar to ambient temperature; And
    The demineralized distillate accumulated in the last flashing step of the multistage flash evaporation system is transferred to the first effect of the multiple effect distillation system at a temperature approximately midway between ambient temperature and the maximum allowable temperature,
    Successive flashing in the multi-effect distillation system to exit the last effect at a temperature very close to the sensible heat and ambient temperature of the distilled water.
    Combination of multiple effect distillation and multistage flash evaporation system.
  2. The method of claim 1,
    Each of the flashing and condensing steps comprises a flash chamber and a condenser, the condenser having at least one conduit having an inlet and an outlet, the at least one conduit passing through the plurality of flash chambers.
    Combination of multiple effect distillation and multistage flash evaporation system.
  3. The method of claim 2,
    Means for extracting a volume of seawater from an external source, passing it through the last condenser, and supplying the volume of seawater under pressure through at least one conduit, the means having an inlet to the at least one conduit In fluid communication with
    Combination of multiple effect distillation and multistage flash evaporation system.
  4. The method of claim 3,
    The brine heater further comprises means for heating the volume of seawater after the volume of seawater has been delivered through the at least one conduit and prior to injection into the flashing and condensation stages.
    Combination of multiple effect distillation and multistage flash evaporation system.
  5. The method of claim 4, wherein
    Means for extracting demineralized distillate from the last stage of the multi-stage flash evaporation system, wherein the volume of heated seawater injected into the plurality of flash chambers is flashed with steam in the plurality of flash chambers, and the steam Condensation at the outer surface of the at least one conduit to form the demineralized distillate
    Combination of multiple effect distillation and multistage flash evaporation system.
  6. The method of claim 5,
    The means for extracting the volume of sea water from an external source and supplying the volume of sea water under pressure through the at least one conduit comprises at least one pump in fluid communication with the inlet of the at least one conduit.
    Combination of multiple effect distillation and multistage flash evaporation system.
  7. The method of claim 6,
    Brine heater for heating the volume of the sea water
    A boiler for delivering a first heating steam to said brine heater after said volume of seawater is preheated by said at least one conduit;
    And a salt water heater in fluid communication with the outlet of said at least one conduit.
    Combination of multiple effect distillation and multistage flash evaporation system.
  8. The method of claim 7, wherein
    And further comprising a first desuperheater in communication with the heater for selectively cooling the first heated steam prior to delivery to the brine heater, wherein the first portion of condensed steam generated by the heater The second portion of the condensation steam produced by the heater and recycled for use in the desuperheater is recycled for use in the boiler.
    Combination of multiple effect distillation and multistage flash evaporation system.
  9. The method of claim 8,
    And further comprising a second desuperheater for selectively cooling the second heating steam generated by the boiler prior to delivery to the first steam of the plurality of condensation and evaporation effects of the multi-effect distillation system.
    Combination of multiple effect distillation and multistage flash evaporation system.
  10. The method of claim 9,
    Further comprising a plurality of supply heaters, each supply heater in communication with at least one conduit and each effect; And
    And further comprising a plurality of flash pots, each flash port communicating with each effect and configured for pressure equalization.
    Combination of multiple effect distillation and multistage flash evaporation system.
  11. The method of claim 5,
    And further comprising a nano filtration membrane pretreatment system for removing hardness ions from the seawater to bring the concentration of sulfate ions to a level consistent with the maximum allowable temperature prior to delivery to the multistage flash evaporation system.
    Combination of multiple effect distillation and multistage flash evaporation system.
  12. The method of claim 11,
    The pretreatment system comprises a nanofiltration membrane system selected from the group consisting of low pressure microfiltration membrane systems, ultrafiltration membrane filtration systems, and combinations thereof.
    Combination of multiple effect distillation and multistage flash evaporation system.
  13. The method of claim 11,
    The pretreatment system further comprises one or more valves for adjusting the flow rate of the seawater stream through the nanofiltration membrane pretreatment system and the flow rate of the remaining seawater stream bypassing the nanofiltration membrane pretreatment system;
    The nanofiltration pretreated stream and untreated bypassing stream are remixed to meet the maximum allowable concentration of sulfate ions matching the maximum temperature.
    Combination of multiple effect distillation and multistage flash evaporation system.
  14. The method of claim 5,
    And further comprising a pump in fluid communication with at least one conduit and inlet to a first of the plurality of condensation and evaporation effects of said multi-effect distillation system, said pump extracting brine from the flash chamber of the last stage of said multistage flash evaporation. Configured to deliver in two parts under pressure,
    A first portion mixed with the incoming seawater to maintain the flow rate needed to circulate in the multistage flash evaporation system for continuous desalting, and a second portion passing through the first effect of the multi-effect distillation system for further desalting sign
    Combination of multiple effect distillation and multistage flash evaporation system.
  15. The method of claim 5,
    Said plurality of said multiple effects distillation system for reheating said latent heat of said vapor in said last effect to reheat said brine transferred to said first effect of said multiple effect distillation system in said last flash stage of said multiple effect distillation system. Further comprising a thermal steam compressor in fluid communication with the last one of the condensation and evaporation effects.
    Combination of multiple effect distillation and multistage flash evaporation system.
  16. The method of claim 5,
    The brine heater for heating the volume of the brine
    A mechanical steam compressor in fluid communication with a last one of said plurality of flash evaporation steps for delivering steam generated in said final flash evaporation step to said brine heater as a first heating steam, said volume of brine by said at least one conduit. Recycling the latent heat of the steam to heat the volume of brine after this heating;
    The brine heater is in fluid communication with the outlet of the at least one conduit.
    Combination of multiple effect distillation and multistage flash evaporation system.
  17. The method of claim 16,
    And a desuperheater for selectively cooling the heated steam prior to transferring the heated steam to the brine heater.
    Combination of multiple effect distillation and multistage flash evaporation system.
  18. The method of claim 17,
    The desuperheater is in communication with the brine heater and at least a portion of the condensed vapor produced in the brine heater is recycled for use in the desuperheater.
    Combination of multiple effect distillation and multistage flash evaporation system.
  19. The method of claim 18,
    And further comprising a pretreatment system for filtering the volume of seawater prior to delivery to the multi-stage flash evaporation system.
    Combination of multiple effect distillation and multistage flash evaporation system.

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4330373A (en) * 1980-07-25 1982-05-18 Aqua-Chem, Inc. Solar desalting plant
WO2006021796A1 (en) * 2004-08-27 2006-03-02 O.H.D.L. Optimised Hybrid Desalination Limited Msf distillate driven desalination process and apparatus
US20100078306A1 (en) * 2008-09-29 2010-04-01 Majed Moalla Alhazmy Multi-stage flash desalination plant with feed cooler
US20150175422A1 (en) * 2012-08-06 2015-06-25 Nippon Soda Co., Ltd. Method for producing bis(halosulfonyl)amine
WO2015154142A1 (en) * 2014-04-11 2015-10-15 Murdoch University System and method for desalination

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015095695A2 (en) * 2013-12-20 2015-06-25 Massachusetts Institute Of Technology Thermal desalination for increased distillate production

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4330373A (en) * 1980-07-25 1982-05-18 Aqua-Chem, Inc. Solar desalting plant
WO2006021796A1 (en) * 2004-08-27 2006-03-02 O.H.D.L. Optimised Hybrid Desalination Limited Msf distillate driven desalination process and apparatus
US20100078306A1 (en) * 2008-09-29 2010-04-01 Majed Moalla Alhazmy Multi-stage flash desalination plant with feed cooler
US20150175422A1 (en) * 2012-08-06 2015-06-25 Nippon Soda Co., Ltd. Method for producing bis(halosulfonyl)amine
WO2015154142A1 (en) * 2014-04-11 2015-10-15 Murdoch University System and method for desalination

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